1. Field of the Invention
This invention relates in general to speed governors or control systems for motor vehicles, and in particular to a circuit for testing such a system to determine whether or not it is operable.
2. Description of the Prior Art
This invention deals with the testing of speed control systems for motor vehicles, usually called cruise controls. These systems operate from the engine vacuum and have a vacuum servo which will pull the throttle of the carburetor open with increased vacuum. The position of the vacuum servo is controlled by a vacuum valve, which is connected to the intake manifold, and a vent valve, which opens the servo to atmosphere to reduce the vacuum and to decrease the speed. A speed sensor monitors the actual speed of the vehicle and supplies a signal to an electronic control module. The control module will control the opening and closing of the vacuum and vent valve solenoids according to the speed selected by a speed selector switch.
Many of these systems are installed on vehicles after the vehicles have been shipped from the factory. One prior art method of testing such a system installed away from the factory, is to actually test drive the vehicle. Test driving is time consuming and expensive. Also, in certain installation areas, such as a shipping port, there may be inadequate space at the port to bring the vehicle up to cruising speed to test the system. If the system is defective, determining the point of trouble is not easy. Continuity can be checked on the wires leading to the various electrical components. However, a defect could be in a solenoid valve, a switch, or in the control module. Often, finding the defect requires trial and error substitution of the various components.